Experimental study on supercooled phase change material for photothermal conversion and long-term thermal energy storage

Due to its intermittent and unreliable nature, solar energy alone cannot meet the continuous demand for thermal energy. While conventional thermal storage systems can help bridge this gap, there is an increasing need for high-performance thermal storage materials and effective thermal insulation. This study introduces an innovative composite phase change material (CPCM) capable of efficiently harnessing sunlight for photothermal conversion. It can maintain stable supercooling in low-temperature environments and release heat through controlled triggering. This CPCM utilizes sodium acetate trihydrate (SAT) as the core salt hydrate, sodium carboxymethyl cellulose (CMC) as a thickener, and expanded graphite (EG) as a thermal conductor and photothermal conversion enhancer. The optimal composition was found to be SAT with 3 wt% CMC and 1 wt% EG, resulting in a phase change temperature of 56.6 degrees C and a latent heat value of 230.43 kJ/kg. CPCM exhibits enhanced phase stability and can be stably supercooled above 35 degrees C. Compared to pure SAT, its photothermal conversion efficiency improved dramatically by 85 %, in addition, the thermal conductivity of CPCM which is 0.794 (W/m & sdot;k) was slightly improved by 16.4 %. The newly developed supercooled CPCM with integrated photothermal storage, as presented in this paper, can directly harness sunlight to absorb and store heat at low temperatures, while releasing it in a controlled manner, after triggering the heat release, the temperature rises by 57 degrees C. The incorporation of CMC and EG into the hydrated salt PCM enhances both the degree of supercooling and the photothermal conversion efficiency, offering a promising solution for household solar thermal collection and long-term heat storage.